Color reproduction system and color conversion profile creation device

Abstract

The color tone of the subject is reproduced or restored with high precision on the display device. [Solution] The color reproduction system comprises a digital camera 1 that captures an image of a subject 6, a color processing device 3 that converts the captured image data 3B into display image data 3C according to a color conversion profile 3A, and a monitor 2 that receives the display image data 3C from the color processing device 3 and displays the image of the subject 6A. The color conversion profile 3A is created using a color chart image obtained by capturing a color chart image displayed on the monitor 2 using the digital camera 1, and converts the captured RGB values ​​of the digital camera 1 to the display RGB values ​​of the monitor 2 so that the color tone of the subject 6 is restored in the color tone of the image of the subject 6A displayed on the monitor 2.

Description

Technical Field

[0001] This invention relates to a color reproduction system and a color conversion profile creation device.

Background Art

[0002] Patent Document 1 discloses a profile creation system that simultaneously photographs a chart printed on a print medium and a chart displayed on a monitor with a digital camera, and creates a color characteristic profile of the digital camera and a color characteristic profile of the monitor. Both the color characteristic profile of the digital camera and the color characteristic profile of the monitor define the correspondence between RGB values and Lab values. By converting the RGB values of a photographed image by the digital camera into Lab values according to the color characteristic profile of the digital camera (device profile of the digital camera), and converting the Lab values into RGB values of the monitor display image according to the color characteristic profile of the monitor (device profile of the monitor), color matching between the digital camera and the monitor is performed.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

[0004] Since Lab values are a device-independent color space, color matching between various digital cameras and various monitors can be achieved by interposing Lab values in color matching between a digital camera and a monitor. However, digital cameras and monitors used in studios and the like are often specific ones, and it is rare to replace the digital camera or monitor every time shooting is done. Also, since data interpolation processing is generally performed when defining the correspondence between RGB values and Lab values (creating a color characteristic profile), when color matching is performed using two color characteristic profiles, it means that data interpolation processing is substantially performed twice on the image data.

[0005] Device link profiles are sometimes used to match colors between two devices without the need for Lab values. Using device link profiles reduces the data interpolation process for image data to a single step, resulting in higher color conversion accuracy. However, device link profiles are often created by combining multiple device profiles. This can sometimes prevent the full potential of digital cameras and monitors from being utilized. [Overview of the Initiative] [Problems that the invention aims to solve]

[0006] This invention aims to reproduce or restore the color tone of a subject with high accuracy when displaying the subject image on a display device, by making full use of the performance of the imaging device and the display device used.

[0007] This invention also aims to create a color conversion profile that fully utilizes the performance of the imaging device and display device used. [Means for solving the problem]

[0008] The color reproduction system according to this invention comprises an imaging device that images a subject and outputs image data representing the subject image, a color conversion device that converts the image data output from the imaging device into display image data according to a color conversion profile, and a display device that receives the display image data provided by the color conversion device and displays the subject image represented by the display image data. The color conversion profile is created using a color chart image obtained by imaging a color chart image displayed on the display device using the imaging device, and the system converts the RGB values ​​of the image data output from the imaging device to the RGB values ​​of the display image data input to the display device so that the color tone of the subject is restored to the color tone of the subject image displayed on the display device. The imaging device uses sensors such as CCD (charge-coupled device) and CMOS (complementary metal-oxide-semiconductor) to read light information and record (output) the image as digital data.

[0009] A color chart image is acquired by the imaging device by capturing the color chart image displayed on the display device. In the color conversion device, a color conversion process is performed using a color conversion profile to convert the RGB values ​​of the captured image data output from the imaging device to the RGB values ​​of the display image data provided to the display device. Since the color conversion profile is created according to a specific display device (a display device used to display the color chart image) and a specific imaging device (an imaging device used to capture the color chart image displayed on the display device), it can fully utilize the performance of the specific display device and the specific imaging device. Furthermore, since the color conversion profile is a so-called device link profile, the color tone of the subject can be reproduced or restored with high accuracy in the image of the subject displayed on the display device, and an image of the subject with a color tone close to the actual color tone of the subject can be displayed on the display device.

[0010] In one embodiment, the color conversion profile is created based on the RGB values ​​of the image data representing each patch image included in the color chart image data output from the imaging device, which is generated by providing the display device with image data representing a color chart composed of multiple patches with different colors and brightnesses, where the RGB values ​​of each patch are known, and capturing the color chart image displayed on the display device using the imaging device. The RGB values ​​of each patch in the known color chart are then used to create the color conversion profile. Even if the color tone of the subject image represented by the image data output from the imaging device is different from the color tone of the subject (object being photographed), this difference can be corrected (restored).

[0011] Preferably, the RGB values ​​(R, G, and B values) of 90% or more of the patch images included in the color chart image are within the range of "minimum value + 1" to "maximum value - 1". If the RGB values ​​are each represented by 8 bits, "minimum value + 1" is 1 and "maximum value - 1" is 254. If the RGB values ​​are each represented by 14 bits, "minimum value + 1" is 1 and "maximum value - 1" is 16382. This is to ensure that color chart images with excessive color saturation are not used to create color conversion profiles, thereby fully utilizing the performance of the imaging and display devices. Since color saturation can be reduced by increasing the shutter speed of the imaging device, if the RGB values ​​of more than 10% of the patch images included in the color chart image are at the minimum value (0) or the maximum value (255 if 8 bits), the shutter speed of the imaging device is set to, for example, one step faster.

[0012] More preferably, the color chart image includes a white patch image, and the RGB values ​​of the white patch image are greater than or equal to "maximum value × 1 / 2". If the RGB values ​​are each represented by 8 bits, "maximum value × 1 / 2" is 127.5, so the RGB values ​​will be 128 or greater. If the RGB values ​​are each represented by 14 bits, "maximum value × 1 / 2" is 8,191.5, so the RGB values ​​will be 8,192 or greater. This is to ensure that color chart images with excessively narrow color gamuts are not used to create color conversion profiles, thereby making full use of the performance of the imaging and display devices. The color gamut can be widened by slowing down the shutter speed of the imaging device, so if the RGB values ​​(any of the R, G, and B values) of the white patch image are less than "maximum value × 1 / 2", the shutter speed of the imaging device is set to, for example, one step slower.

[0013] In one embodiment, an ISO sensitivity of 400 or less is set for the imaging device from among the multiple ISO sensitivities that can be set for the imaging device. This is because the color reproduction system (imaging device) is basically used indoors and images stationary subjects are captured, so there is basically no need to amplify the signal. By setting the ISO sensitivity of 400 or less for the imaging device, subjects and color chart images can be captured with less noise, and it is also expected that the accuracy of the color conversion profile created using the captured color chart image will be improved.

[0014] In other embodiments, the imaging device is set to an aperture that captures the subject image with the least amount of blur among the apertures that can be set on the imaging device. This allows the imaging device to output a subject image with a clear outline (color chart image).

[0015] In yet another embodiment, a booth is provided equipped with a lighting fixture for illuminating the subject, and a color sample installed in the booth is captured using the imaging device under the illumination of the lighting fixture. A color gamut determination means is provided to determine whether the RGB values ​​of the color sample image, represented by the color sample image data output from the imaging device, fall within the range of the captured RGB values ​​of the color chart image. If the color gamut determination means determines that at least a portion of the RGB values ​​of the color sample image are outside the range of the captured RGB values ​​of the color chart image, an illumination setting means is provided to adjust the illumination of the lighting fixture so that the values ​​fall within the range. This makes it possible to capture subject images with little to no overexposure, or subject images with little to no underexposure.

[0016] Preferably, the system includes a second display device different from the display device used for displaying a color chart image for creating a color conversion profile, and both the first and second display devices are calibrated. By providing display image data to the second display device, it is possible to display an image of the subject with a color tone close to the subject's color tone not only on the display device used for displaying the color chart image, but also on the second display device.

[0017] In one embodiment, the color chart image for creating a color conversion profile is also displayed on a second display device different from the display device that displays the color chart image for creating a color conversion profile, and the color chart image displayed on the second display device is captured by the imaging device. A means is further provided for creating a calibration profile to match the color tone of the second display device to the color tone of the first display device, based on the color chart image acquired by capturing the color chart image displayed on the first display device with the imaging device, and the second color chart image acquired by capturing the color chart image displayed on the second display device with the imaging device. The color tone of the other display device (second display device) can be matched to that of the display device that displays the color chart image for creating a color conversion profile, using the display device that displays the color chart image for creating a color conversion profile as a reference (reference display device).

[0018] This invention also provides a color conversion profile creation device. The color conversion profile creation device according to this invention includes an acquisition means that displays a color chart image on a display device, which represents a color chart comprising a plurality of patches with different colors and brightnesses, and the RGB values ​​of each patch are known, and acquires a color chart image by capturing the displayed color chart image using an imaging device; and a color conversion profile creation means that creates a color conversion profile that converts the image RGB values ​​of the image data output from the imaging device to the display RGB values ​​of the display image data input to the display device, based on the RGB values ​​of each patch image data that constitutes the color chart image and the RGB values ​​of each patch, so that the color tone of the subject is restored to the color tone of the subject image displayed on the display device. A color conversion profile that fully utilizes the performance of the imaging device and the display device used can be created. [Brief explanation of the drawing]

[0019] [Figure 1] This is a block diagram illustrating the hardware configuration of the color reproduction system. [Figure 2] This section provides a schematic overview of the pre-processing steps performed in the imaging system. [Figure 3] It is a flowchart showing the preprocessing flow. [Figure 4] It is a flowchart showing the preprocessing flow. [Figure 5] It is a flowchart showing the preprocessing flow. [Figure 6] It is a flowchart showing the preprocessing flow. [Figure 7] It shows the TC9.18 RGB color chart. [Figure 8] It is an RGB distribution diagram representing the color gamut of the TC9.18 RGB color chart imaging image captured by a digital camera with the shutter speed set to 1 / 8 second. [Figure 9] It is an RGB distribution diagram representing the color gamut of the TC9.18 RGB color chart imaging image captured by a digital camera with the shutter speed set to 1 / 6 second. [Figure 10] It is an RGB distribution diagram showing the RGB values of the imaging image when the color sample is captured by a digital camera with the illuminance of the LED set to 1000 lux, and the RGB values of the color chart imaging image superimposed. [Figure 11] It is an RGB distribution diagram showing the RGB values of the imaging image when the color sample is captured by a digital camera with the illuminance of the LED set to 800 lux, and the RGB values of the color chart imaging image superimposed. [Figure 12] It is a flowchart during the operation of the color reproduction system. [Figure 13] It is a flowchart showing the preprocessing flow of other embodiments. [Figure 14] It is a flowchart showing the preprocessing flow of other embodiments.

Modes for Carrying Out the Invention

[0020] FIG. 1 is a block diagram schematically showing the hardware configuration of the color reproduction system.

[0021] A color reproduction system is a system that displays a subject image (an image representing a subject) created by capturing a subject on a monitor, and is designed to reproduce (restore) the subject's color tone (color and brightness) on the monitor as accurately as possible.

[0022] A color reproduction system is used in print inspections to verify whether printed materials (gravure or offset printed) containing images of subjects, such as food ingredients, have the intended color tones. By using a color reproduction system, instead of directly checking the gravure or offset printed materials at the printing plant, it is possible to remotely verify whether the printed materials have the intended color tones based on the subject image displayed on a monitor. In addition to print inspections, a color reproduction system can also be used when performing remote color matching of products (color matching based on color samples of products with target colors, color matching of products and product samples, etc.).

[0023] The color reproduction system consists of an imaging system and an observation system. The imaging system and the observation system are connected via a network, such as the Internet, and are configured to send and receive data from each other.

[0024] The imaging system includes a digital camera (imaging device) 1 for imaging the subject (an object whose color tone should be checked, such as a printed document) 6, a monitor (display device) 2 for displaying a subject image 6A representing the subject 6, a color processing device (color conversion device) 3 for performing color conversion processing described later, and a booth 4 that illuminates the subject 6 with high color rendering LEDs (light-emitting diodes) 5 and blocks out external light. The subject 6 is placed inside the booth 4 and imaged by the digital camera 1 under illumination by the high color rendering LEDs 5. The subject 6 and the color sample may be placed side by side inside the booth 4 and both may be imaged simultaneously with the digital camera 1, or the subject 6 and the color sample may be imaged separately with a time delay.

[0025] The observation system includes a monitor 7 that displays the subject image 6A, a computer device 8 that receives display image data 3C representing the subject image 6A transmitted from the imaging system (color processing device 3), which is obtained by color-converting the imaging image data 3B output from the digital camera 1 in the imaging system according to a color conversion (color characteristic) profile 3A, and provides the display image data 3C to the monitor 7, and a booth 4 equipped with high color rendering LEDs 5. If a color sample 6' is available on the observation side, the color tone of the color sample 6' and the color tone of the subject image 6A can be compared on the observation side.

[0026] In this embodiment, the description assumes that the captured image data 3B and the display image data 3C are 8-bit (256 gradations each for R, G, and B). Of course, it is also possible to handle image data with 12-bit, 14-bit, or other bit counts.

[0027] In order to reproduce (restore) the color tone of subject 6 as accurately as possible in the subject image 6A displayed on monitors 2 and 7, the color processing device 3 of the shooting system converts the captured image data 3B output from the digital camera 1 into display image data 3C for display on monitor 2 using a color conversion profile 3A. Details of the color conversion profile 3A and the process for creating the color conversion profile 3A will be described later.

[0028] Display image data 3C is provided to monitor 2 of the imaging system and monitor 7 of the observation system. Although monitor 2 and monitor 7 are separate monitors, by pre-calibrating both monitors 2 and 7, the same color tone can be reproduced on both monitor 2 and monitor 7 based on the same image data.

[0029] Figure 2 schematically shows the pre-processing performed on the imaging system prior to the operation of the color reproduction system that captures subject 6. Figures 3 to 6 are flowcharts showing the pre-processing flow.

[0030] Referring to Figure 2, the preprocessing is performed using a booth 4 equipped with a digital camera 1, monitor 2, color processing device 3, and LED 5, which constitute the imaging system.

[0031] Preprocessing is basically performed by the color processing unit 3 controlling the operation of the shooting system. The color processing unit 3 is a computer device that includes a CPU (Central Processing Unit) that comprehensively controls the operation of the entire device, memory that provides a work area, buffer area, etc., an operating system, a program that creates color conversion profiles (described later), data representing pattern images and color chart images displayed on the monitor 2, a storage device 9 that stores the created color conversion profiles, etc., and a transmitting and receiving device that sends and receives data. As described below, the operation of the digital camera 1, monitor 2, and booth 4 (LED 5) is controlled based on the data created or calculated in the color processing unit 3.

[0032] Referring to Figure 3, the pre-processing performed before operating the color reproduction system includes calibration processing of monitors 2 and 7 (step 20), imaging condition setting processing of digital camera 1 (step 30), color conversion profile creation processing (step 40), and illumination setting processing of LED 5 (step 50).

[0033] First, monitors 2 and 7 are calibrated (step 20). As monitors 2 and 7 are used, their white color temperature and brightness will gradually change. In addition, there are individual differences in color between monitors 2 and 7. Monitors 2 and 7 are calibrated to ensure that the same colors are displayed on both monitors when given the same image data.

[0034] Monitors 2 and 7 are calibrated with a target color reproduction point (white point, black point, color gamut, gamma value, color temperature, etc.). For example, with a colorimeter placed on monitors 2 and 7, white, black, red, green, blue, etc. are displayed on monitors 2 and 7, and the colorimeter is used to measure the colorimetric values ​​(CIE XYZ values). For example, the color adjustment (RGB adjustment) of monitors 2 and 7 is performed so that the chromaticity coordinates of the colorimetric value of white measured by the colorimeter become x=0.3127, y=0.3290, z=0.3583. If monitors 2 and 7 are color adjusted based on a lookup table (LUT) stored in the color processing device 3 (or monitors 2 and 7 themselves), the LUT values ​​are rewritten after calibration.

[0035] Next, the process of setting the imaging conditions for digital camera 1 proceeds (step 30).

[0036] Figure 4 shows the details of the imaging condition setting process for digital camera 1.

[0037] First, the ISO sensitivity to be set for digital camera 1 is determined (step 31).

[0038] The ISO sensitivity of the digital camera 1 is selected from several ISO values ​​that can be set in the digital camera 1, such as auto, 100, 125, 160, ..., 400, ..., 1000, ..., 10000, .... The color reproduction system is generally used indoors, and the subject 6 captured by the digital camera 1 is stationary, so signal amplification is not particularly necessary. For this reason, the lowest ISO sensitivity that can be set in the digital camera 1, such as ISO 100, is determined to be the ISO sensitivity to be set in the digital camera 1. However, even if the ISO sensitivity is not the lowest, an image of the subject with little noise can be captured if the ISO is 400 or lower. The determined ISO sensitivity is given from the color processing device 3 to the digital camera 1 and set in the digital camera 1.

[0039] Next, the process proceeds to determine the aperture (F-number) to be set on the digital camera 1 (steps 32-34).

[0040] In the aperture determination process, image data of a checkerboard pattern stored in the memory device 9 of the color processing device 3 is provided to the monitor 2, so that the checkerboard pattern image is displayed on the monitor 2 (step 32), and the checkerboard pattern image displayed on the monitor 2 is captured by the digital camera 1 (step 33).

[0041] The aperture (F-number) that minimizes blur in the checkerboard pattern image acquired by capturing the checkerboard pattern image displayed on monitor 2 with digital camera 1 is determined by the color processing device 3 as the aperture (F-number) to be set on digital camera 1 (step 34). This is to sharply reproduce the outline of the subject image 6A displayed on monitor 2 during system operation. The checkerboard pattern image displayed on monitor 2 is captured multiple times with different apertures (F-numbers) on digital camera 1, and the aperture used to acquire the image with the least blur among the multiple checkerboard pattern images obtained by capturing is determined as the aperture to be set on digital camera 1.

[0042] Images with little blur have strong edges, while blurred images have weak edges. By differentiating each of multiple checkerboard pattern images, a score representing the degree of edge sharpness can be calculated for each of the multiple checkerboard pattern images. The checkerboard pattern image with the highest score can be determined to be the one with the least blur.

[0043] Multiple checkerboard pattern images captured by the digital camera 1 with different apertures may be displayed side-by-side on the monitor 2. The operator may then select the checkerboard pattern image with the least blur and determine that the aperture (F-number) used to acquire the selected checkerboard pattern image is the aperture (F-number) to be set on the digital camera 1.

[0044] Instead of using a checkerboard pattern image, a striped pattern image representing vertical or horizontal stripes, or a minimal character image may be used.

[0045] The determined aperture (F-number) is provided from the color processing device 3 to the digital camera 1 and set on the digital camera 1.

[0046] After the aperture is set, proceed to determine the shutter speed (steps 35-37).

[0047] In the shutter speed determination process, a color chart, such as a TC9.18RGB color chart, is used. Image data representing the TC9.18RGB color chart stored in the memory device 9 of the color processing device 3 is provided to the monitor 2, and the TC9.18RGB color chart image is displayed on the monitor 2 (step 35). The monitor 2 displaying the TC9.18RGB color chart image is captured by the digital camera 1 (step 36).

[0048] Using multiple shutter speeds that can be set in the digital camera 1, the monitor 2 displaying the TC9.18RGB color chart image is captured multiple times with different shutter speeds. From the multiple TC9.18RGB color chart images acquired, the image that does not show color saturation and was captured at the maximum (longest) (slowest) shutter speed is selected, and the shutter speed at which that image was captured is determined to be the shutter speed to be set in the digital camera 1 (step 37).

[0049] Figure 7 shows the TC9.18RGB color chart 10. Figure 8 is an RGB distribution diagram representing the color gamut of the TC9.18RGB color chart image captured by digital camera 1 with a shutter speed set to 1 / 8 second. Figure 9 is an RGB distribution diagram representing the color gamut of the TC9.18RGB color chart image captured by digital camera 1 with a shutter speed set to 1 / 6 second.

[0050] The TC9.18RGB color chart 10 consists of 918 rectangular patches 11, each with different color and / or brightness. Each patch 11 has different RGB values ​​(a set of R, G, and B values), allowing the TC9.18RGB color chart 10 to represent 918 different RGB values. However, instead of a color chart 10 where all patches 11 have different RGB values, a color chart with some patches 11 having the same RGB values ​​can also be used.

[0051] Comparing Figures 8 and 9, when the shutter speed is set to 1 / 8 second, the TC9.18RGB color chart image acquired by capturing the TC9.18RGB color chart image displayed on monitor 2 with digital camera 1 shows that none of the R, B, or G values ​​have reached their maximum value (255), and all colors are represented (Figure 8). In contrast, when the shutter speed is set to 1 / 6 second, the R and B values ​​reach their maximum value (255), resulting in color saturation. To prevent color saturation, i.e., loss of color information, the shutter speed used to acquire the TC9.18RGB color chart image without color saturation is considered a candidate shutter speed to be set on digital camera 1.

[0052] The faster the shutter speed, the less likely color saturation is to occur. However, the faster the shutter speed, the narrower the color gamut (color space) becomes (the maximum value moves away from 255), and the tonal range of the captured image deteriorates. To avoid narrowing the color gamut too much, the maximum (slowest) shutter speed within the range where color saturation does not occur is determined as the shutter speed to be set on the digital camera 1. This allows for the reproduction of the tonal range of the subject image 6A during operation as finely as possible.

[0053] As described above, the TC9.18RGB color chart 10 is composed of numerous patches 11 that differ in color and brightness from one another. The RGB values ​​of each of the numerous patch images included in the TC9.18RGB color chart image obtained by capturing the TC9.18RGB color chart image displayed on the monitor 2 with the digital camera 1 are acquired. If the RGB values ​​of 90% or more of the patch images are in the range of 1 to 254 (values ​​other than 0 and 255) ("minimum value + 1" to "maximum value - 1"), the color chart image may be judged as not saturated. Also, if the RGB values ​​of each of the white patch images among the numerous patch images are 128 or more ("maximum value × 1 / 2" or more), the color gamut of the color chart image can be judged as relatively wide. The shutter speed to be set in the digital camera 1 is determined by the color processing device 3 when acquiring an image in which the RGB values ​​of 90% or more of the patch images are between 1 and 254, and the RGB value of the white patch image is the maximum (128 or more).

[0054] The determined shutter speed is also provided from the color processing device 3 to the digital camera 1 and set on the digital camera 1.

[0055] Instead of the color processing device 3 providing the ISO sensitivity, aperture, and shutter speed (imaging conditions) to the digital camera 1, the operator may set the imaging conditions to the digital camera 1. By setting the imaging conditions determined as described above to the digital camera 1, the display performance of the monitor 2 that displays the subject image 6A during operation can be utilized to the greatest extent possible.

[0056] Once the imaging conditions (ISO sensitivity, aperture, and shutter speed) are set, the process proceeds to create a color conversion profile (step 40).

[0057] Referring to Figure 5, the color chart data for creating a color conversion profile stored in the storage device 9 of the color processing device 3 is provided to the monitor 2, so that a color chart image is displayed on the monitor 2 (step 41). The monitor 2 on which the color chart image is displayed is then captured by the digital camera 1 under the ISO sensitivity, aperture (F-number), and shutter speed set as described above (step 42). The same TC9.18RGB color chart image used in the shutter speed determination process can be used for the color chart image displayed on the monitor 2.

[0058] As described above, the TC9.18RGB color chart 10 contains 918 patches 11 that differ in color and brightness from one another, and the RGB values ​​of the 918 patches 11 are known (stored in the storage device 9 of the color processing device 3). The known RGB values ​​of each patch 11 (hereinafter referred to as "color chart RGB values") are read from the storage device 9 (step 43). In parallel with this, the RGB values ​​of each patch image in the color chart image, represented by the color chart image data acquired by the digital camera 1 (the average value of the RGB values ​​of multiple pixels constituting the patch image) (hereinafter referred to as "image RGB values") are acquired (step 44). The color chart RGB values ​​and the image RGB values ​​are used to create a color conversion profile (device link profile) 3A between the digital camera 1 and the monitor 2, as described below.

[0059] First, the color chart RGB values ​​and the image RGB values ​​are mapped to each patch (Step 45). Table 1 shows the correspondence between the color chart RGB values ​​and the image RGB values ​​for each patch.

[0060] [Table 1]

[0061] For example, among the multiple patches 11 included in the color chart 10, the image RGB values ​​corresponding to the black patch (R, G, and B values ​​are all 0) (patch ID: 1) are not necessarily all 0. The same applies to the image RGB values ​​corresponding to the white patch (R, G, and B values ​​are all 255) (patch ID: 918). The creation of the color conversion profile is performed by associating the color chart RGB values ​​for each of the 918 patches 11 with what image RGB values ​​they will be in the digital camera 1, and then inversely calculating the color chart RGB values ​​corresponding to various image RGB values ​​in the digital camera 1 according to this association (step 46). This makes it possible to convert the RGB values ​​of the image represented by the image data output from the digital camera 1 into RGB values ​​that more accurately represent (reproduce, restore) the color of the subject 6 on the monitor 2.

[0062] Table 2 shows an example of the color conversion profile 3A that is created.

[0063] [Table 2]

[0064] The color conversion profile 3A in this embodiment includes 91,125 different (ID: 0 to 91124) imaging RGB values, each with R, G, and B values ​​varying in pixel value increments of "5.8". The corresponding 91,125 color chart RGB values ​​are calculated according to the correspondence between the color chart RGB values ​​and imaging RGB values ​​shown in Table 1. While there are 918 correspondences shown in Table 1, there are 91,125 correspondences shown in Table 2. Therefore, interpolation operations, such as linear interpolation, nonlinear multiple regression interpolation, or interpolation using a neural network algorithm, are performed in the process of calculating the correspondences in Table 2 from the correspondences in Table 1.

[0065] Color conversion profile 3A is used for color conversion processing when displaying the subject image 6A, which represents the subject 6 captured by the digital camera 1, on the monitor 2. In the following, the RGB values ​​corresponding to each of the 91,125 different imaging RGB values ​​obtained by varying the values ​​of each imaging RGB value in increments of pixel value "5.8" in color conversion profile 3A, which are used to more accurately represent the color tone of the subject 6 as the subject image 6A on the monitor 2, are referred to as "RGB values ​​for monitor display".

[0066] As described above, the created color conversion profile 3A is created based on the digital camera 1, which has imaging conditions set to make the most possible use of the display performance of monitor 2. Therefore, it can reproduce the color tone of the subject image 6A displayed on monitor 2 as accurately as possible.

[0067] Finally, proceed to setting the brightness of LED5 (Step 50).

[0068] Referring to Figure 6, under lighting of a predetermined illuminance (e.g., 1000 lux) by LED 5, the subject (color sample) placed inside booth 4 is imaged by digital camera 1 (step 51). The color sample can be a printed color chart, an object to be photographed during operation, white paper, synthetic paper, or tiles.

[0069] Image data of a color sample output from the digital camera 1 is provided to the color processing device 3, and it is determined whether the RGB values ​​are within the range of the RGB values ​​of the color chart image (step 52).

[0070] Figure 10 is an RGB distribution diagram showing the RGB values ​​of the captured image and the color gamut of the color chart image when the illuminance of LED 5 is set to 1000 lux and a color sample is captured by digital camera 1. Figure 11 is an RGB distribution diagram when the illuminance of the LED is set to 800 lux.

[0071] Referring to Figure 10, when the illuminance of LED 5 is set to 1000 lux, the plot of RGB values ​​representing the captured color sample image (represented by numerous small dots in Figure 10) extends beyond the upper left of the RGB value range of the captured color chart image (the roughly trapezoidal gray area in Figure 10). This means that saturation (so-called overexposure) occurred when the color sample was captured under a relatively bright illuminance of 1000 lux. Referring to Figure 11, when the illuminance of LED 5 is set to 800 lux, the plot representing the captured color sample image stays within the RGB value range of the captured color chart image. This means that if the illuminance is reduced to 800 lux, saturation (overexposure) does not occur when the color sample is captured by the digital camera 1.

[0072] Although not shown in the diagram, if the illumination of LED5 is insufficient and the image is dark, the plot of RGB values ​​representing the color sample image may extend beyond the range of RGB values ​​of the color chart image towards the lower right. This means that saturation (so-called black crushing) occurred because the color sample was imaged under relatively low illumination.

[0073] Returning to Figure 6, if saturation occurs (NO in step 52), it is determined whether it is positive saturation (overexposure) (corresponding to the upper left direction in the RGB distribution diagrams of Figures 10 and 11) or negative saturation (underexposure) (corresponding to the lower right direction in the RGB distribution diagrams of Figures 10 and 11) (step 53). If it is positive saturation, the illuminance of LED 5 is reduced (positive direction in step 53, step 54). If it is negative saturation, the illuminance of LED 5 is increased (negative direction in step 53, step 55). If saturation does not occur, the pre-configuration process is completed (YES in step 52).

[0074] Figure 12 is a flowchart showing the operation of the color reproduction system.

[0075] Referring to Figure 1, the subject (object to be photographed) 6 is placed inside the booth 4, and the subject 6 is photographed by the digital camera 1 under the illumination of the LED 5 (step 61). Image data 3B representing the subject image 6A is obtained.

[0076] In the color processing device 3, the captured image data 3B is converted to display image data 3C according to the color conversion profile 3A described above (step 62). Display image data 3C, which represents the subject image 6A using monitor display RGB values ​​instead of the captured RGB values, is provided to the monitor 2. The subject image 6A, which reproduces the color tone of the subject 6 as accurately as possible, is displayed on the monitor 2.

[0077] The display image data 3C is transmitted via the Internet to a computer device 8 at a remote location (observation system) as needed (step 64), and the subject image 6A is displayed on a monitor 7 connected to the computer device 8. A color sample 6' is set up in the booth 4 at the remote location as needed, and the color sample 6' is illuminated by an LED 5 (the LED 5 is set to the same illuminance as when the subject 6 is imaged in the imaging system). The color tone of the color sample 6' and the color tone of the subject image 6A displayed on the monitor 7 can be compared at the remote location. By calibrating the monitor 7 of the observation system in the same way as the monitor 2 of the imaging system, the color tone of the subject image 6A displayed on the monitor 2 and the color tone of the subject image 6A displayed on the monitor 7 can be made the same.

[0078] As described above, monitor 2 of the shooting system and monitor 7 of the observation system can be accurately calibrated by measuring the color of monitor 2 and monitor 7 respectively using a colorimeter, and adjusting the colors with a target color reproduction point as the goal. This allows the color tones of the two monitors, 2 and 7, to be matched (aligned).

[0079] Instead of using a colorimeter to calibrate both monitors 2 and 7, you can also match the color tone of monitor 7 (a different monitor from monitor 2) on the observation system to the color tone of monitor 2 on the shooting system by using a color chart image used, for example, when setting the imaging conditions of digital camera 1 (step 30 in Figure 3) and when creating a color conversion profile (step 40 in Figure 3). In the following description, the monitor used for setting the imaging conditions of digital camera 1 and creating a color conversion profile (monitor 2 on the shooting system) will be referred to as "color reference monitor 2," and the other monitor that can be matched to the color tone of color reference monitor 2 (monitor 7 on the observation system) will be referred to as "color adjustment monitor 7" to distinguish them.

[0080] Figure 13 shows a pre-processing flowchart for matching the color tone of the color adjustment monitor 7 to the color tone of the color reference monitor 2. Figure 14 is a flowchart detailing the calibration process of the color adjustment monitor 7. In Figure 13, the same reference numerals are used for processes identical to those in the flowchart shown in Figure 3, and redundant detailed explanations are omitted.

[0081] The color reference monitor 2 is calibrated (step 20). As described above, the color reference monitor 2 is color-adjusted so that, for example, the colorimetric value of white measured by a colorimeter becomes a predetermined value.

[0082] The imaging conditions for digital camera 1, namely ISO sensitivity, aperture, and shutter speed, are set (steps 30, 31, 34, 36).

[0083] After setting the imaging conditions for digital camera 1 (step 30), the color adjustment monitor 7 is calibrated (step 60). Note that the calibration of the color adjustment monitor 7 can be performed at any time after setting the imaging conditions for digital camera 1. That is, it can be done after creating the color conversion profile (step 40) or after setting the LEF illumination (step 50).

[0084] Referring to Figure 14, the color chart image used to determine the shutter speed is displayed on the color reference monitor 2, and the color chart image displayed on the color reference monitor 2 is captured by the digital camera 1 with the imaging conditions (ISO sensitivity, aperture, shutter speed) already set (steps 61, 62).

[0085] A color adjustment monitor 7 is installed in place of the color reference monitor 2, and the aforementioned color chart image is displayed on the newly installed color adjustment monitor 7. The color chart image displayed on the color adjustment monitor 7 is then captured under the same conditions by a digital camera 1 with pre-set imaging conditions (steps 63, 64). Since the conditions are the same, for example, the distance between the color reference monitor 2 and the digital camera 1 is the same as the distance between the color adjustment monitor 7 and the digital camera 1.

[0086] Similar to the process for creating the color conversion profile described above, a calibration profile (lookup table) for matching the color tone of the color adjustment monitor 7 to the color tone of the color reference monitor 2 is created in the color processing device 3 (step 65). The color conversion profile described above is created by mapping color chart RGB values ​​to image RGB values ​​for each patch (step 45), and then inversely calculating the color chart RGB values ​​corresponding to various image RGB values ​​in the digital camera 1 according to this mapping (step 46). However, the calibration profile is created by mapping color chart images (color reference monitor image RGB values) obtained by imaging the color chart image displayed on the color reference monitor 2 to color chart images (color adjustment monitor image RGB values) obtained by imaging the color chart image displayed on the color adjustment monitor 7 to color chart images for each patch, and then inversely calculating the color reference monitor image RGB values ​​corresponding to various color adjustment monitor image RGB values ​​according to this mapping. Similar to the process for creating the color conversion profile described above, the calibration profile is completed by interpolation operations, such as linear interpolation, nonlinear multiple regression interpolation, or interpolation using a neural network algorithm.

[0087] The created calibration profile is set on the color adjustment monitor 7 (step 66). This allows the color tones of the two monitors 2 and 7 to be matched, even if the color reference monitor 2 and the color adjustment monitor 7 differ in, for example, manufacturer, model, manufacturing date, and usage time.

[0088] A color adjustment monitor 7, whose color tones have been adjusted based on the color reference monitor 2, is used as a component of the observation system (see Figure 1).

[0089] The color adjustment monitor 7 is synchronized with the color reference monitor 2 at the facility equipped with the imaging system, and then transported to the facility equipped with the observation system. Of course, it is also possible to bring the digital camera 1, with its imaging conditions set at the imaging system facility, to the observation system facility, and create a calibration profile at the observation system facility, which is located separately from the imaging system, to match the color tone of the color adjustment monitor 7 with the color tone of the color reference monitor 2. [Explanation of symbols]

[0090] 1. Digital camera (imaging device) 2.7 Monitor (Display Device) 3. Color Processing Equipment (Color Conversion Device) 3A Color Conversion Profile 3B imaging data Image data for 3C display Booths 4 and 9 5 LED 6 Subject 6A Subject image 8. Computer equipment 9 Storage device

Claims

1. An imaging device that captures an image of a subject and outputs image data representing the image of the subject. A color conversion device that converts the captured image data output from the above-mentioned imaging device into display image data according to a color conversion profile, and The device includes a display device that receives display image data from the above-mentioned color conversion device and displays an image of a subject represented by the display image data. The above color conversion profile, This method is created using a color chart image acquired by capturing a color chart image displayed on the above-mentioned display device using the above-mentioned imaging device, and converts the RGB values ​​of the captured image data output from the above-mentioned imaging device to the RGB values ​​of the display image data input to the above-mentioned display device so that the color tone of the subject is restored to the color tone of the subject image displayed on the above-mentioned display device. Color reproduction system.

2. The above color conversion profile, By providing the display device with image data representing a color chart composed of multiple patches with different colors and brightness levels, where the RGB values ​​of each patch are known, the color chart image displayed on the display device is captured using the imaging device, and the image is created based on the captured RGB values ​​of the captured image data representing each patch image included in the captured color chart image data output from the imaging device, and the RGB values ​​of each patch of the known color chart. The color reproduction system according to claim 1.

3. Of the multiple patch images included in the color chart image, 90% or more of the patch images have RGB values ​​within the range of "minimum value + 1" to "maximum value - 1". The color reproduction system according to claim 2.

4. The above color chart image includes a white patch image, and the RGB value of the white patch image is "maximum value × 1 / 2" or greater. The color reproduction system according to claim 2.

5. Of the multiple ISO sensitivities that can be set in the above-mentioned imaging device, an ISO sensitivity of 400 or less is set in the above-mentioned imaging device. The color reproduction system according to claim 1.

6. The aperture that captures the subject image with the smallest blur among the apertures that can be set on the above-mentioned imaging device is set on the above-mentioned imaging device. The color reproduction system according to claim 1.

7. The booth is equipped with lighting fixtures to illuminate the above subject, A color gamut determination means for determining whether the RGB values ​​of the color sample image, represented by the color sample image data output from the imaging device, fall within the range of the RGB values ​​of the color chart image, by imaging the color sample installed in the booth under the illumination of the above-mentioned lighting fixture using the above-mentioned imaging device, and The system includes an illuminance setting means that, when the color gamut determination means determines that at least a portion of the RGB values ​​of the color sample image are outside the range of the captured RGB values ​​of the color chart image, adjusts the illuminance of the lighting fixture so that the values ​​fall within the range. The color reproduction system according to claim 1.

8. It includes a second display device, which is different from the display device used for displaying a color chart image for creating a color conversion profile, Both the above-mentioned display device and the above-mentioned second display device are calibrated. The color reproduction system according to claim 1.

9. An acquisition means for obtaining a color chart image by displaying a color chart image on a display device, which represents a color chart comprising multiple patches of different colors and brightness, with the RGB values ​​of each patch being known, and capturing the displayed color chart image using an imaging device, and The system includes a color conversion profile creation means that creates a color conversion profile that converts the RGB values ​​of the image capture data output from the imaging device to the RGB values ​​of the display image data input to the display device, based on the RGB values ​​of each patch image capture image constituting the above color chart image capture image and the RGB values ​​of each patch, so that the color tone of the subject is restored to the color tone of the subject image displayed on the display device. Color conversion profile creation device.

Images